The present invention relates to an ink-jet printer which performs printing by jetting ink onto a sheet of paper held on a rotary drum as a printing medium.
Recently, personal computers of high performance and low cost have been readily available, and widely spreading rapidly. With this spread, demands for color printers also increase. For personal use, various ink-jet printers have been developed for color printing.
Conventionally, for example, an ink-jet printer capable of printing 500 sheets or more continuously is known. The ink-jet printer includes a hollow rotary drum which rotates at a constant circumferential speed and a print head for jetting color ink to a paper sheet held on the peripheral surface of the rotary drum. The paper sheet is loaded on the rotary drum from the front side thereof and printed in a state wound around the rotary drum. After printing, the paper sheet is removed from the rotary drum to be discharged to the rear side of the rotary drum.
The print head includes, for example, yellow, cyan, magenta, and black nozzle units arranged around the peripheral surface of the rotary drum. Each nozzle unit has a plurality of ink-jet nozzles aligned across the paper sheet in the main scanning direction parallel to the axis of the rotary drum and disperses ink from the ink-jet nozzles with the rotation of the drum. Each nozzle unit is shifted in the main scanning direction at a constant rate for each revolution of the rotary drum, and is returned to a home position after a predetermined number of revolutions which cause the nozzle unit to be moved by a distance equal to the nozzle pitch. Each nozzle unit performs printing of the whole paper sheet by jetting ink in the main scanning direction and the sub-scanning direction perpendicular to the main scanning direction as described above.
It is preferable that the paper sheet is held on the rotary drum in a state where the rotary drum is rotating, and removed from the rotary drum after printing without stopping the rotation of the rotary drum so as to achieve high speed printing. Therefore, a conventional ink-jet printer holds the paper sheet on the rotary drum using negative pressure suction force. In this case, a plurality of suction holes are formed as through holes spread in the entire peripheral surface of the rotary drum. Further, a negative pressure creating section is provided for setting the inside of the rotary drum in a negative pressure state. The paper sheet is held on the peripheral surface of the rotary drum by negative pressure suction force applied thereto through the suction holes. Moreover, the negative pressure suction force is eliminated to remove the paper sheet from the peripheral surface of the rotary drum.
However, in the above-mentioned ink-jet printer, the peripheral surface of the rotary drum may be contaminated when a foreign substance such as ink from an ink nozzle is suctioned by some of the suction holes.